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Title: Comparison of unitary exocytic events in pituitary lactotrophs and in astrocytes: modeling the discrete open fusion-pore states
Author: Kabaso, Doron
Jorgačevski, Jernej
Calejo, Ana I.
Flašker, Ajda
Guček, Alenka
Kreft, Marko
Zorec, Robert
Keywords: astrocytes
capacitance measurements
equivalent circuit
transient fusion-pore
Issue Date: 2013
Publisher: Frontiers Media
Abstract: In regulated exocytosis the merger between the vesicle and the plasma membranes leads to the formation of an aqueous channel (a fusion-pore), through which vesicular secretions exit into the extracellular space. A fusion pore was thought to be a short-lived intermediate preceding full-fusion of the vesicle and the plasma membranes (full-fusion exocytosis). However, transient exocytic events were also observed, where the fusion-pore opens and closes, repetitively. Here we asked whether there are different discrete states of the open fusion-pore. Unitary exocytic events were recorded by the high-resolution cell-attached patch-clamp method in pituitary lactotrophs and brain astrocytes. We monitored reversible unitary exocytic events, characterized by an on-step, which is followed by an off-step in membrane capacitance (C m ), a parameter linearly related to the membrane area. The results revealed three categories of reversible exocytic events (transient fusion-pore openings), which do not end with the complete integration of the vesicle membrane into the plasma membrane. These were categorized according to the observed differences in the amplitude and sign of the change in the real (Re) parts of the admittance signals: in case I events (Re ≈ 0) fusion pores are relatively wide; in case II (Re > 0) and case III (Re < 0) events fusion pores are relatively narrow. We show that case III events are more likely to occur for small vesicles, whereas, case II events are more likely to occur for larger vesicles. Case III events were considerably more frequent in astrocytes than in lactotrophs.
Peer review: yes
DOI: 10.3389/fncel.2013.00033
ISSN: 1662-5102
Appears in Collections:CESAM - Artigos
DBio - Artigos

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